OBJECTIVEDyslipidemia and chronic inflammation are risk factors of cardiac fibrosis. This study was aimed to investigate their possible synergetic effects and underlying mechanisms on progression of cardiac fibrosis in apolipoprotein E knockout (ApoE -/-) mice.

METHODSTwenty-four ApoE-/- mice were divided into normal chow diet (control), high fat diet (HFD group), and HFD plus subcutaneously injection of 10% casein (inflammation group) for 8 weeks. Lipid profile and serum amyloid A (SAA) were examined by clinical biochemical assays and Enzyme-Linked Immunosorbent Assay, respectively. Hematoxylin-eosin staining (HE) and Masson staining were used to evaluate the myocardial accumulation of lipid and collagen. Collagen I protein expression was detected by immunohistochemical staining. Endothelial-to-mesenchymal transition related protein expressions were determined by Western blot.

RESULTSSerum SAA level was significantly higher in inflammation group [(127.42 ± 26.99) ng/ml] than in control [(15.40 ± 7.62) ng/ml] and HFD [(8.17 ± 0.72) ng/ml] group (all P < 0.01).However serum levels of triglyceride, total cholesterol, and low density lipoprotein (LDL) cholesterol were significantly higher in HFD group than in inflammation and control groups[TG (7.53 ± 2.05) mmol/L vs. (3.43 ± 0.79) mmol/L; TC (27.80 ± 3.99) mmol/L vs. (14.94 ± 1.92) mmol/L;LDL-C (11.56 ± 2.56) mmol/L vs. (9.46 ± 1.31) mmol/L, all P < 0.05) . Foam cell formation in cardiac vessels, myocardial collagen deposit, protein expressions of collagen I, CD31, and alpha-smooth muscle actin (α-SMA) were all significantly higher in inflammation group than in HFD group (all P < 0.05) suggesting that inflammation contributes to the phenotype endothelial-to-mesenchymal transition in heart.

CONCLUSIONInflammation exacerbates dyslipidemia mediated cardiac fibrosis in ApoE-/- mice partly through enhancing myocardial endothelial-to-mesenchymal transition.